Amber Heard is taking her role in Aquaman pretty seriously. Her character Mera, Queen of Atlantis, is known for her strength and resilience—something that Heard, given her tumultuous split from ex Johnny Depp, is certainly no stranger to in her real life. But she wanted to take her tenacity a step further. "She wanted to deliver for the character," celebrity trainer Gunnar Peterson (who also works with hot bods of Hollywood Jennifer Lopez and Sofía Vergara) told PEOPLE.

A post shared by Amber Heard (@amberheard) on May 19, 2017 at 11:40am PDT

Peterson was one of several trainers Heard worked with for the film. He said the actress came to him four to five times a week "for a nonstop, no-breaks hour with me, and then she went to her fight training, which was rigorous!" (Related: Peterson Shares the Best Way to Lose Love Handles)

A post shared by Amber Heard (@amberheard) on May 5, 2017 at 8:24am PDT

The workouts focused on full-body fitness and were athletically based, Peterson explained. "We trained movements, not muscles," he said. "Squat presses, sled work, and lots of work in a rotational plane against resistance. She is a true athlete." And while Peterson says the workouts were "unrelenting," he credits Heard's positive attitude and incredible work ethic for the impressive results.(Related: Motivational Quotes to Help Re-Energize Your Fitness Goals)